To support pursuit of the NINDS mission, here we propose to introduce a high-impact novel technology for Imaging to the Washington University Neuroscience community. We intend to provide Core Instrumentation to perform Planar Illumination Microscopy (also known as light sheet microscopy) to catalyze new imaging efforts that aim to monitor large-scale neuronal ensembles. The recent Federal announcement of the Brain Activity Map targets neurophysiology for rapid growth and development in the coming decade. One of the most promising techniques for high-throughput neurophysiology is fluorescence imaging using light sheets. Our implementation, Objective-Coupled Planar Illumination (OCPI) microscopy, achieves imaging speeds that are hundreds or thousands of times faster than two-photon microscopy by simultaneously illuminating all pixels in the objective's focal plane, thereby eliminating the need to collect images by scanning one pixel at a time. The method achieves fast imaging simultaneously with high sensitivity and low phototoxicity and is therefore particularly well-suited to long-term recording periods. The custom-built OCPI instrument will be a Core offering within an existing Imaging Center, the Bakewell Neurolmaging Facility. Therefore, this proposal describes a plan and a schedule by which the new OCPI microscope will be introduced, and the oversight we will establish to ensure that its use is made available fairly and broadly. We also emphasize that we have recent experience in precisely these community-based efforts: we successfully introduced earlier version of this instrumentation as a Core facility and now can foresee the need for more access by a larger community of Neuroscientists to a faster and more flexible version. We plan Facility support for OCPI users that includes a facility manager to provide maintenance and training, a data center for image analysis, and a data manager to help with customized data analysis. We provide a series of quantifiable milestones by which to evaluate progress in offering this new high-impact technology.' By the end of the 4-yr period, we anticipate a steady base of at least 20 different users from across the diverse WU Neuroscience community, and a usage rate at or near full-time.